#include <iostream>
#include <string>

using namespace std;

class Solution
{
public:
    int trailingZeroes(int n)
    {
        int count=0;
        while(n>=5)
            {
                count+=n/5;
                n=n/5;
            }
        return count;
    }
};

int main()
{
    Solution solution;
    int n;
    while(cin>>n)
        {
            cout<<solution.trailingZeroes(n)<<endl;
        }
}